Sequential strategies

Thase, M.E. and Rush, A.J. (1997) When at fitst you don t succeed sequential strategies fot antideptessant nontespondets./ Clin Psychiatry 58 23—29. 

Those who fail to respond to an SSRI may respond to a TCA, and vice versa. Thus, these two broad-spectrum classes can be used in a sequential strategy to adequately treat the majority of cases. However, many physicians try another newer antidepressant (e.g, venlafaxine, bupropion, nefazodone) in such patients because of the safety and tolerability problems associated with TCAs. Of note, the tolerability profile of secondary amine TCAs such as desipramine is as favorable as any of the newer antidepressants and probably better than nefazodone. Nevertheless, the secondary amine TCAs have a therapeutic index as narrow as tertiary amine TCAs (e.g., amitriptyline, imipramine) in terms of lethality in overdoses resulting from cardiotoxicity. 

Thase ME, Rush AJ. When at first you don t succeed sequential strategies for antidepressant nonresponders. J Clin Psychiatry 1997 58 23-29. 

The sequential strategies for investigating d-SoCs that follow from the systems approach are outlined below. These strategies are idealistic and subject to modification in practice. 

In the sequential strategy, a control (manipulated) variable profile is discretized over a time interval. The discretized control profile can be represented as a piecewise constant, a piecewise linear, or a piecewise polynomial function. The parameters in such functions and the length of time subinterval become decision variables in optimization problem. This strategy is also referred to a control vector parameterization (CVP). 

Bernardo, M.C., Buck, R., Liu, L., Nazaret, W.A., Sacks, J., and Welch, W.J. (1992). Integrated circuit design optimization using a sequential strategy. IEEE Transactions on Computer-Aided Design, 11, 361-372. 

Sequential strategies for discrimination can be risky if applied before a thorough enumeration of plausible model forms. Important regions of experimentation may then be missed, and the kinds of models needed to describe those regions may go undiscovered. Factorial experimentation at the outset is desirable to allow inductive building of good model forms. 

Strategies used for optimization of selectivity can basically be divided into three separate groups (a) the simultaneous strategy, (b) the sequential strategy, and (c) the interpretative strategy. 

A CCD for three factors is listed in Table 4, and includes an imbedded 2 factorial design with center points and three pairs of star points. For rotatability, a = 1.682, as there are F = 8 factorial points in the design. A three-block sequential strategy for a three-factor CCD is listed in Table 5, where ... 

With our sequential strategy using a small number of glycosyl donors 4-8 as building blocks, an automated solid-phase synthesis of these biologically important compounds was possible [13]. 

The proteom analysis of HIV-1 virion is a five-step sequential strategy as shown in Fig. 1. The five steps of this strategy are ... 

Sequential strategies of optimization are based on an initial design of an experiment followed by a sequence of further measurements in the direction of the steepest ascent or descent. That is, no quantitative relationship between factors and responses is evaluated, but the response surface is searched along an optimal (invisible) path. The two strategies are exemplified in Figure 4.1. 

The optimized parameters of problem 6.13 are listed in the third column of table 6.5. By comparing the TAC of both approaches, it can easily been inferred that the simultaneous optimization of both spatial and control structures leads to a cheaper and more controllable process than that obtained via the conventional sequential strategy. Although the relative difference between both economic indexes is fairly small, the accumulative cost saving sums up to 0.2 million euros per year. This cost reduction is predominantly originated from the reduced column diameter and smaller reboiler. 

Each problem in this book is designed to illustrate a sequential strategy of thinking to solve a question of the type Provide a plausible explanation of the following interconversion in your answer, include mechanisms for each reaction step . A typical example is ... 

The sequential strategy involves linearisation of the model at any point z " of a sequence of approximations. Let thus z = z " and compute the Af-vector (residual)... 

To implement the deterministic optimization approach, the sequential strategy proposed by Li et al. (1998) is used, where the whole algorithm is divided into one optimization layer with SQP as a standard NLP solver and one simulation layer, where all dependent variables are computed through an integration step. The model is a large scale DAE system which is discretized with collocation on finite elements. The whole batch time is discretized into 30 time intervals. The control variables are set as piecewise constants. The computed trajectories of the control variables for the optimal operation are illustrated in Fig. 1. 

In a sequential strategy only a few experiments at a time are carried out and, on the basis of the results, the experiment to be carried out next is defined. These designs are used when the optimum of a single response is the only information desired. The best known sequential method is called the simplex method. However, it does not provide much information about a model relating the response with the factors studied. Despite the fact that it would be possible to map part of the response surface (the route followed to reach the optimum), the model obtained would not necessarily be a good one to describe the whole response surface and that is the reason why, when a model of the response surface is needed, one should prefer simultaneous methods. There are several situations where sequential designs are not suitable. One of them is when more than one response needs to be optimized. It also happens that these methods are trapped on a local optimum, and do not find the global optimum. 

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